mc68331cpv20b1 Freescale Semiconductor, Inc, mc68331cpv20b1 Datasheet - Page 54

• Manufacturer Part Number: mc68331cpv20b1
• Description: Mc68331 32 Bit Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

4
To obtain clock frequency in kilohertz, find counter modulus in the left column, then multiply reference frequency by value
in appropriate prescaler cell.
4-12
SYNCR Y field determines the count modulus for a modulo 64 down counter, causing
it to divide by a value of Y + 1. When W or Y values change, VCO frequency changes,
and there is a VCO relock delay. The SYNCR X bit controls a divide-by-two circuit that
is not in the synthesizer feedback loop. When X = 0 (reset state), the divider is en-
abled, and system clock frequency is one-fourth VCO frequency; setting X disables
the divider, doubling clock speed without changing VCO speed. There is no relock de-
lay when clock speed is changed by the X bit.
Clock frequency is determined by SYNCR bit settings as follows:
The reset state of SYNCR ($3F00) produces a modulus-64 count.
For the device to perform correctly, system clock and VCO frequencies selected by
the W, X, and Y bits must be within the limits specified for the MCU. Do not use a com-
bination of bit values that selects either an operating frequency or a VCO frequency
greater than the maximum specified values in APPENDIX A ELECTRICAL CHARAC-
TERISTICS.
Table 4-7 shows clock control multipliers for all possible combinations of SYNCR bits.
Table 4-8 shows clock frequencies available with a 32.768-kHz reference and a max-
imum specified clock frequency of 20.97 MHz.
Modulus
000000
000001
000010
011111
000011
000100
000101
000110
000111
001000
001001
001010
001011
001100
001101
001110
001111
010000
010001
010010
010011
Y
[W:X] = 00
Freescale Semiconductor, Inc.
F
For More Information On This Product,
12
16
20
24
28
32
36
40
44
48
52
56
60
64
68
72
76
80
84
SYSTEM
Table 4-7 Clock Control Multipliers
4
8
SYSTEM INTEGRATION MODULE
Go to: www.freescale.com
=
F
REFERENCE
[W:X] = 01
104
112
120
128
136
144
152
160
168
16
24
32
40
48
56
64
72
80
88
96
8
Prescalers
4 Y
+
1
[W:X] = 10
2
2W
112
128
144
160
176
192
208
224
240
256
272
288
304
320
336
16
32
48
64
80
96
+
X
USER’S MANUAL
[W:X] = 11
128
160
192
224
256
288
320
352
384
416
448
480
512
544
576
608
640
672
32
64
96
MC68331